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Biomedical subjects

F Cervero

Publications and source records attributed to F Cervero.

At least 91 records · Page 5Linked to original sources
PubMed1984

Cutaneous inputs to dorsal horn neurones in adult rats treated at birth with capsaicin.

Single unit electrical activity has been recorded from dorsal horn neurones in the lumbar spinal cord of adult rats which had been treated at birth with either capsaicin (50 mg kg-1) or with the solvent-vehicle only. The responses of these neurones to electrical stimulation of A- and C-fibres in the sural nerve and to natural stimulation of their cutaneous receptive fields have been studied. In vehicle-injected rats, 54% of the units driven by electrical stimulation of the A-fibres in the sural nerve could also be driven by stimulation of the C-fibres in this nerve. In capsaicin-treated animals, only 30% of such units had a C-fibre input from the sural nerve. In vehicle-injected rats, 51.5% of the neurones with a C-fibre input showed a 'wind-up' effect on repetitive C-fibre stimulation of the sural nerve at 1 Hz. A similar proportion of neurones (55%) displayed this effect in capsaicin-treated rats. There were fewer neurones with very intense 'wind-up' in capsaicin-treated compared to vehicle-treated rats. In capsaicin-treated animals, greater proportions of neurones with 'wind-up' were superficially located in the dorsal horn, had small receptive fields and were driven only by cutaneous nociceptors. The proportions of neurones driven by innocuous mechanical stimulation of the skin, by noxious mechanical stimulation or by both forms of stimulation were similar in vehicle-injected and capsaicin-treated animals. In capsaicin-treated rats, more neurones had 'medium-sized' receptive fields than in vehicle-injected rats. In capsaicin-treated rats, more neurones had receptive fields in the foot and ankle than in vehicle-injected animals, where receptive fields in the toes were predominant. Some neurones showed expanded receptive fields after repetitive electrical stimulation of C-fibres at 1 Hz. This expansion occurred more often in neurones recorded from capsaicin-treated animals than in those of vehicle-injected rats. These results are discussed in relation to the role of afferent C-fibres in sensory mechanisms.

Afferent Pathways↗
PubMed1984

Fine afferent fibers from viscera do not terminate in the substantia gelatinosa of the thoracic spinal cord.

Transganglionic transport of horseradish peroxidase (HRP) has been used to study the anatomy of the central projection of somatic and visceral afferent fibers to the thoracic spinal cord of the cat. A dense concentration of somatic afferent fibers and terminals was found in laminae I and II of the dorsal horn and more scattered terminals were present in laminae III, IV and V and in Clarke's column. In contrast, visceral afferent fibers and terminals were found only in lamina I or reaching lamina V via a small bundle of fibers located in the lateral border of the dorsal horn. These results indicate that fine afferent fibers from viscera, unlike those of cutaneous origin, do not project to the substantia gelatinosa (lamina II) of the dorsal horn.

Afferent Pathways↗
PubMed1984

Dorsal root potentials are unchanged in adult rats treated at birth with capsaicin.

The possible contribution of non-myelinated afferent fibres (C fibres) to the mechanisms of primary afferent depolarization (p.a.d.) in the spinal cord of the rat has been investigated. Dorsal root potentials (d.r.p.s.) were recorded in the lumbar cord of normal adult rats, of adult rats which had been injected at birth with a solution of capsaicin (50 mgkg-1 s.c.) and of adult rats which had been injected at birth with the drug vehicle only. D.r.p.s were recorded from the dorsal rootlet that entered the spinal cord in the main area of termination of the tibial nerve. The location of this area was assessed by mapping the spinal cord in the rostro-caudal axis while recording cord dorsum potentials evoked by A-fibre volleys from the tibial nerve. No differences in peak amplitude, area or time to peak amplitude were observed between the d.r.p.s evoked in control and capsaicin-treated rats by stimulation of the tibial, sural or common peroneal nerves. The relation between the size of incoming A volleys to the spinal cord and the size of the d.r.p.s evoked by them was unaffected by the neonatal capsaicin treatment. Rats treated at birth with capsaicin showed a virtual absence of afferent C fibres as assessed from the lack of C waves in the compound action potentials evoked in each of the three nerves studied after antidromic stimulation of the dorsal roots. The presence of p.a.d. in control and in capsaicin-treated animals was also established using the technique of excitability testing of primary afferent fibres (Wall, 1958). No differences were observed between the p.a.d. recorded in control and in capsaicin-treated animals using this technique. D.r.p.s and p.a.d. (assessed by excitability testing of primary afferent fibres) were of similar magnitude in control and in capsaicin-treated rats anaesthetized with either sodium pentobarbitone or urethane. It is concluded that p.a.d. of myelinated afferent fibres produced by incoming volleys in myelinated afferent fibres is not affected by a life-long loss of non-myelinated afferent fibres.

Animals↗
PubMed1983

Supraspinal connections of neurones in the thoracic spinal cord of the cat: ascending projections and effects of descending impulses.

Single unit electrical activity has been recorded extracellularly from 103 neurones in the thoracic spinal cord of decerebrate cats. The responses of these neurons to electrical stimulation of cutaneous and visceral afferent fibres, their projection through ascending sensory pathways and the effects of descending impulses on the neurones have been studied. Of the 103 neurones recorded, 45 (43.7%) responded only to activation of cutaneous afferent fibres ('Somatic' neurones). Their recording sites were located mainly in laminae II, III and IV of the dorsal horn. The remaining 58 neurones (56.3%) responded to stimulation of cutaneous and visceral afferent fibres ('Viscero-somatic' neurones). Their recording sites were located in laminae I, V, VII and VIII of the grey matter. Sixteen neurones had axons projecting through ascending pathways: 6 were post-synaptic dorsal column cells (PSDC), 2 were spino-cervical tract cells (SCT), 5 projected through the contralateral ventro-lateral funiculus (VLQ) and 3 through the ipsilateral dorso-lateral funiculus (DLF). All PSDC cells were somatic and all VLQ neurones were viscero-somatic. Reversible spinalization of the animals by cold block resulted in a selective increase of the responses of viscero-somatic neurones to cutaneous and visceral C-fibre input. In some viscero-somatic neurones, cold block induced a reduction or abolition of the visceral input suggesting its mediation via supraspinal loops. Electrical stimulation of the ipsilateral DLF evoked non-specific inhibitions of all inputs to viscero-somatic neurones. These results are discussed in relation with the mechanisms of visceral sensation.

Afferent Pathways↗
PubMed1983

Somatic and visceral inputs to the thoracic spinal cord of the cat: effects of noxious stimulation of the biliary system.

1. Single unit electrical activity has been recorded extracellularly from 133 neurones in the grey matter of the 8th and 9th thoracic segments of the spinal cord in chloralose anaesthetized cats. The responses of these neurones to electrical stimulation of the ipsilateral splanchnic nerve, to natural stimulation of the skin and to distension of the biliary system have been studied.2. Of the neurones studied, 75% responded to electrical stimulation of the splanchnic nerve and had a cutaneous receptive field in the costal region (viscero-somatic neurones). Twenty-three per cent of the neurones had a cutaneous receptive field but no visceral input (somatic neurones) and 2% had a visceral input but no cutaneous field.3. Somatic neurones had well-localized receptive fields from which they could be driven by innocuous stimulation of the skin (52%), by noxious (7%) or by both forms of stimulation (41%). No somatic neurones projected to supraspinal levels via the contralateral ventro-lateral funiculus.4. Viscero-somatic neurones were excited by small myelinated and non-myelinated afferent fibres in the splanchnic nerve. Most viscero-somatic neurones had cutaneous inputs from nociceptors either exclusively (38%) or in addition to non-noxious inputs (53%).5. The recording sites of somatic neurones were located almost exclusively in laminae II and IV and dorsal V of the dorsal horn. In contrast, viscero-somatic neurones were located in lamina I and in laminae V-IX of the grey matter. No differential distribution of recording sites according to type of cutaneous receptive field has been found within the viscero-somatic group of neurones.6. About one-third of all viscero-somatic neurones could be excited by distensions of the biliary system. In all cases, intensities of visceral stimulation above physiological levels were necessary to activate the neurones. Most units driven by biliary afferents were located in or ventral to lamina V of the dorsal horn. The excitation of these units by biliary distension was found to be specifically mediated by receptors in the biliary system.7. Sixteen per cent of the neurones were found to project to supraspinal levels via crossed ventro-lateral pathways. All of these neurones were viscero-somatic with axonal conduction velocities between 12 and 68 m sec(-1).8. These results are discussed in relation to the postulates of the ;Convergence-projection' theory of referred pain.

Action Potentials↗
PubMed1982

Noxious intensities of visceral stimulation are required to activate viscerosomatic multireceptive neurons in the thoracic spinal cord of the cat.

Single unit electrical activity has been recorded from neurons in the Th8 and Th9 segments of the spinal cord in chloralose-anesthetized cats. These neurons had cutaneous receptive fields in the right costal region from which they could be driven by noxious and/or innocuous stimulation of the skin. They could also be activated by distensions of the biliary system but only at noxious intensities of visceral stimulation. No viscero-somatic convergent neurons has been found responding to innocuous visceral stimulation.

Afferent Pathways↗
PubMed1982

Neonatal capsaicin does not affect unmyelinated efferent fibers of the autonomic nervous system: functional evidence.

Visceral nociceptive thresholds, viscero-visceral reflexes and the effects of efferent stimulation of autonomic nerves has been studied in adult rats treated at birth with capsaicin. These animals showed visceral analgesia and depressed visceral reflexes. However, stimulation of unmyelinated efferent fibers in autonomic nerves produced normal effects. It is concluded that neonatal treatment with capsaicin destroys selectively unmyelinated afferent fibers.

Animals↗
PubMed1982

Afferent activity evoked by natural stimulation of the biliary system in the ferret.

A technique for the natural stimulation of the biliary system which permits the distinction between noxious and innocuous intensities of stimulation has been developed in the ferret. Male ferrets anaesthetized with urethane have been used. Controlled distensions of the biliary system were produced and the nociceptive nature of the stimulus was ascertained by reflex increases in blood pressure. Levels of biliary pressure that did not evoke changes in blood pressure were considered innocuous. Using this approach electrical activity has been recorded from biliary afferents. Thirty-two recordings were obtained. Twenty-one were of afferents that could be excited by innocuous levels of biliary pressure (low threshold afferents) and 10 recordings were of afferents excited only by noxious stimulation of the biliary system (high threshold afferents). One fibre could not be activated by changes in biliary pressure. Twenty-seven receptive fields were located: 12 in the gallbladder and 15 in the biliary ducts. The relevance of high threshold biliary receptors to visceral nociception is discussed.

Afferent Pathways↗
PubMed1982

Influence of neonatally administered capsaicin on baroreceptor and chemoreceptor reflexes in the adult rat.

1 Baroreceptor and chemoreceptor reflex activity was studied in anaesthetized adult rats which had been treated neonatally with a single injection of capsaicin (50 mg/kg s.c.). 2 Pressor responses to bilateral carotid artery occlusion were significantly lower in capsaicin-treated rats compared with vehicle-treated controls. Pressor responses to intravenously injected noradrenaline were similar in the two groups of rats. 3 Resting respiratory minute volume and tidal volume were lower in anaesthetized capsaicin-treated animals than in vehicle-treated controls, but there was no significant difference in respiratory frequency. 4 The increases in respiration evoked by intravenous administration of the peripheral arterial chemoreceptor stimulant, sodium cyanide, or by breathing a hypoxic gas mixture, were significantly lower in capsaicin-treated rats compared with the controls. 5 It is concluded that baroreceptor and chemoreceptor reflex activity are significantly reduced in anaesthetized adult rats which had been treated neonatally with capsaicin, and that this is likely to result from the destruction of unmyelinated baro- and chemoreceptor afferent fibres.

Animals↗
PubMed1981

Neonatal capsaicin and thermal nociception: a paradox.

Thermal and mechanical nociceptive thresholds and somato-visceral reflexes have been studied in normal rats and in rats treated neonatally with capsaicin. Mechanical nociceptive thresholds were increased in capsaicin treated rats whereas thermal nociceptive thresholds remained unchanged. In contrast, somato-visceral reflexes evoked by thermal noxious stimulation of the skin could not be elicited in capsaicin treated rats whereas mechanical noxious stimulation was effective in evoking visceral reflexes.

Animals↗
PubMed1981

Intracellular marking of identified neurones in the superficial dorsal horn of the cat spinal cord.

Intracellular iontophoresis of horseradish peroxidase has been used to mark identified neurones in the superficial dorsal horn of cats. The cats were anaesthetized with alpha-chloralose and paralysed with gallamine triethodide. Four specific nocireceptive neurones in the marginal zone and seven neurones in the substantia gelatinosa were recovered. One of the former and four of the latter are described in detail and are illustrated as reconstructions from serial sections. The results confirm previous conclusions that the substantia gelatinosa contains neurones classified as 'inverse' and that the nocireceptive neurones of lamina I are Waldeyer Cells.

Animals↗
PubMed1979

Ascending projections of nociceptor-driven Lamina I neurones in the cat.

Single unit activity has been recorded from nociceptor-driven Lamina I neurones in the lumbar spinal cord of chloralose anaesthetized and gallamine paralysed cats. Ninety-four nociceptor-driven Lamina I neurones were identified by their superficial location in the dorsal horn and their ability to respond only to noxious stimulation of their cutaneous receptive fields. One-third of the Lamina I neurones responded only to noxious mechanical stimulation of the skin (Class 3a) and two-thirds responded to both mechanical and thermal noxious stimulation (Class 3b). Lissauer's tract was stimulated electrically two and three segments rostral to the recording sites. Ninety percent of the neurones tested showed a post-synaptic excitation mediated by fibres conducting at a mean velocity of 5.2 m/s (range 0.9--13.3 m/s). It is concluded that A delta and C afferent fibres running in Lissauer's tract excite nociceptor-driven Lamina I neurones. Ninety-six percent of the neurones tested showed a long period of inhibition (100--200 ms) following stimulation of large afferent fibres in the dorsal column. This inhibition was increased when the intensity of stimulation recruited Lissauer's tract fibres. Fifteen percent of the neurones tested were antidromically activated by Lissauer's tract stimulation from up to 3 segments rostal to their origin. A further 18.5% were antidromically excited by stimulation of deeper tracts. The mean conduction velocity of the axons of these projecting neurones was 8.6 m/s (range 3.8--16.5 m/s) and thus are small myelinated axons. The Class 3b neurones exhibited a significantly lower conduction velocity (7.5 +/- 2.8 (S.D.) m/s) than the Class 3a neurones (10.7 +/- 3.7 (S.D.) m/s). It is concluded that at least two-thirds of the population of nociceptor-driven Lamina I neurones are segmental interneurones.

Afferent Pathways↗